164 FXUS61 KPBZ 240601 AFDPBZArea Forecast Discussion National Weather Service Pittsburgh PA 201 AM EDT Wed Sep 24 2025
.SYNOPSIS... Periodic precipitation chances will continue through the week with seasonable temperatures. Mainly dry conditions should return this weekend.
&&
.NEAR TERM /THROUGH TODAY/... KEY MESSAGES:
- Dense fog in spots north of PGH this morning - Shower/thunder chances increase again this morning with another shortwave. Possible instances of flooding. ---------------------------------------------------------------
A weak shortwave ridge crossing the region early this morning has ended any shower activity. With the limited cloud coverage early this morning, recent rainfall, and light winds, areas of fog have developed. Issued a dense fog advisory for PA counties north of Pittsburgh given available surface observations and satellite data. Currently it is effect until 9AM, but it is possible we will be able to pare it back as cloud coverage increases from the west. Overall, morning fog is expected to dissipate between by mid-morning.
A sfc low is then progged to cross north across the forecast area over the course of the afternoon. Effective shear values will increase, CAPE values will still be relatively low, but given the setup, cannot rule out a few strong storms. However, the severe potential looks less likely this afternoon. Piggybacking on the above, latest ensemble guidance shows joint probabilities of 0% to 25% of CAPE>500j/kg and shear>30kts during the day. SPC has removed the "Marginal" risk previously in place over portions of the forecast area and went with just general thunder with their latest update.
&&
.SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/... KEY MESSAGES:
- Flood threat continues overnight - Rain and thunderstorm chances continue Thursday ----------------------------------------------------------------
Rain chances will persist into early Thursday under deep southwest flow as the upper low meanders over the Great Lakes. Strengthening jet dynamics across West Virginia and western Pennsylvania may enhance rainfall rates, leading to periods of heavy rain Thursday morning. Isolated areas could receive 1-2 inches of rain in 6 hours. Given this potential, the Weather Prediction Center (WPC) has placed portions of region under a "Marginal" to "Slight" risk for flooding.
&&
.LONG TERM /FRIDAY THROUGH TUESDAY/... KEY MESSAGES:
- Light showers expected Friday - A building ridge will likely support warm and drier conditions over the weekend ------------------------------------------------------------------
Behind the departing trough and cold front, the risk for heavy rainfall will diminish as drier mid and upper-level air moves in. A few isolated showers may develop early Friday, mainly across the higher terrain due to lingering low-level moisture and upsloping as winds shift from the northwest.
Looking ahead, ensemble guidance consistently indicates a ridge building over the region Sunday into Monday. This setup will likely bring drier conditions along with temperatures trending warmer than average.
&&
.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... A band of showers/embedded thunderstorms associated with a 700mb shortwave will continue to weaken and exit the region through 02Z. A period of mostly VFR conditions should ensue/continue into the overnight hours under brief, temporary ridging.
There is fairly high confidence in the development of IFR/LIFR flight conditions overnight, but there is still some uncertainty whether these restrictions will manifest more as low stratus or fog. Given the moist surface, nearly calm wind, and elevated dewpoints, any prolonged clearing should result in the development of IFR/LIFR fog, while increasing high clouds may lead to favoring an IFR/LIFR stratus deck. For now, favoring fog more than stratus between 06Z and 14Z.
Modest improvement to low MVFR is possible with some weak mixing. MVFR ceilings will likely linger through the day. The next shortwave and a NE lifting surface warm front is expected during the day Wednesday, aiding another round of convection during the afternoon. Have used PROB30 groups for both the initial showers and likely later convection. IFR impacts are possible in brief heavy rain, with gusty wind also possible.
.OUTLOOK.... Similar diurnal trends with rounds of rain can be expected for Thursday into Friday morning before an upper trough axis finally shifts east of the region. There is then increased confidence in a drier weekend period with longer intervals of VFR conditions.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES... PA...Dense Fog Advisory until 9 AM EDT this morning for PAZ007>009- 013>016-020-022-077-078. OH...None. WV...None.
&&
$$
SYNOPSIS...88 NEAR TERM...88 SHORT TERM...Hefferan/88 LONG TERM...Hefferan/88 AVIATION...CL
NWS PBZ Office Area Forecast Discussion